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RT GPU Distributed Rendering on two PCs is slower than on just one PC ???

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  • RT GPU Distributed Rendering on two PCs is slower than on just one PC ???

    I've just added a new machine to my set up and have been doing some testing, using the latest project I recently worked on - and am getting surprising results which are leaving me a bit disappointed !

    My first PC, a 5960x, has 4 x 1080ti's, and before I built my new PC, it was rendering this project, on all 4 GPUs, at 1m 56s, locally.

    Adding my new machine (a 7980xe), which has become my main machine, it has 2 x 1080ti's, and it was RT rendering on 2 GPU's at 2m 11, locally.

    Now, they are connected via a very simple Windows HomeGroup Network, and the same scene yields surprising results......

    When both are working together (distributed rendering) RT, just on GPUs alone (all 4 + 2), the render time is 1m 51s.......

    That's just marginally quicker than the sole 5960x on its own....

    When both are rendering with GPU *and* CPU, the render time is fractionally better, by around 1 or 2 seconds.....

    But when I retry rendering via the network, disabling all devices on the 7980xe, so it was using just the 5960x as a slave, the render was taking just 1m 46s.......

    As I was watching the temperatures etc via the Corsair Link software, I could see;

    When all 6 GPU's were used to create the scene, the GPU's weren't being stressed and the temperatures were mid-50's to mid-60's.

    But when only one machine was being used in the rendering, the temperatures on the GPU's were much higher (and what I'm used to seeing when rendering - ie around 70++)

    It looks to me, that the more GPU's you have, the less stress the GPU are put under - at the expense of render times.

    If I just use one machine, it's as though *then* the GPU's are being pushed.
    Jez

    ------------------------------------
    3DS Max 2023.3.4 | V-Ray 6.10.08 | Phoenix FD 4.40.00 | PD Player 64 1.0.7.32 | Forest Pack Pro 8.2.2 | RailClone 6.1.3
    Windows 11 Pro 22H2 | NVidia Drivers 535.98 (Game Drivers)

    Asus X299 Sage (Bios 4001), i9-7980xe, 128Gb, 1TB m.2 OS, 2 x NVidia RTX 3090 FE
    ---- Updated 06/09/23 -------

  • #2
    When you use all 6 GPU's the temperature is lower probably because not all of them are utilised at 100%.
    The reason for this may be that much of the image is background and because V-Ray is smart enough to know that there is no need to sample those parts of the image that are no necessary like background.
    You may end up with a small part of the image that needs sampling (rendering) and if the Ray bundle size is too high not all of your GPU's will be able to acquire part of the image for rendering, respectively not all of them will be utilised at 100%.
    If this is your case, decrease the Ray bundle size. It will decrease the render time and increase the utilisation of the GPU's.
    If this does not help you, please send us your scene along with all assets used in, to support@chaosgroup.com. So we can investigate the issue more closely.
    Hristo Dimitrov | chaos.com
    Chaos Cosmos Representative | cosmos.chaos.com

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    • #3
      Thanks Hristo,

      It's working correctly - the strange results were due to a bitmap not being loaded and therefore giving inconsistent results - my apologies.
      Jez

      ------------------------------------
      3DS Max 2023.3.4 | V-Ray 6.10.08 | Phoenix FD 4.40.00 | PD Player 64 1.0.7.32 | Forest Pack Pro 8.2.2 | RailClone 6.1.3
      Windows 11 Pro 22H2 | NVidia Drivers 535.98 (Game Drivers)

      Asus X299 Sage (Bios 4001), i9-7980xe, 128Gb, 1TB m.2 OS, 2 x NVidia RTX 3090 FE
      ---- Updated 06/09/23 -------

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